B. skeletal and nervous system
I believe the correct answer is "Carbon dioxide"
Answer:
Sample 4.
Explanation:
Oxygen is very important for life, so this should be present.
For starters, humans have feelings and cells. If we get hurt we can feel things such as pain unlike a tent. If you hit a tent there is nothing it feels because it has no feelings. We have cells all through our body and rocks don't. They are made of other stuff but not cells.
